Polymorphonuclear (PMN) Leukocytes

  • PMNs are composed of three cell types; neutrophils, eosinophils and basophils, based on their staining characteristics with certain dyes.
  • Also called granulocytes since they consist of many granules consisting lytic enzymes.
  • These cells are predominantly important in the removal of bacteria and parasites from the body.
  • They engulf these foreign bodies and degrade them using their powerful enzymes.
  • Multi-lobed nucleus, 11-14 μm
  • 50-70% of circulating WBC (higher numbers suggestive of bacterial infection)
  • 7-10 hours in circulation and then migrate to tissue, life 3-4 days
  • The fine granules stain poorly with acidic and basic dyes neutrophil.
  • Phagocytosis and killing of ingested microorganisms.
  • Granules contain bactericidal enzymes; eg. Lysozyme, myeloperoxidase; neutral proteases (i.e. elastase); acid hydrolases (B-glucoronidase), collagenase and lactoferrin and cathepsin B.
  • The phagosome fuses with granules to destroy internalized bacteria by oxygen dependent respiratory burst.
  • Neutrophils are the 1st cells to arrive. A number of substances produced during an inflammatory response recruit neutrophils to a site of inflammation.
  • Represent 1-3% of circulating WBCs, 11-15 μm
  • Possess a bi-lobed nucleus and a heavily granulated cytoplasm.
  • Granules stain orange/red with the acidic dye Eosin Y.
  • Somewhat phagocytic but DO NOT act as APCs.
  • The major role of the eosinophil is believed to be against parasites, particularly parasitic worms.
  • Eosinophils kill by ADCC [antibody dependent cell-mediated cytotoxicity] by binding to parasite – specific IgE via cell surface
  • When eosinophils bind to IgE on the surface of a worm, the cell is triggered to degranulate. The contents of the granules cause
    damage to the worm’s tegument.
  • One component unique to the eosinophils – and highly toxic to worms – Major Basic Protein (MBP).
  • Only present in the bloodstream, and represent 0.2 % of circulating WBC
  • Lobed nucleus – more variable, large coarse granules stain blue with basic dye methylene blue.
  • They play a major role in the allergic response when they release their granules (containing histamine, serotonin, heparin, prostaglandin, etc into the bloodstream following exposure to specific allergens).
  • Basophils bear Fc receptors for IgE (FceRs)
  • When an individual is exposed to an allergen, allergen specific IgE is produced. This IgE binds to the surface of basophils [in the sensitization phase of the allergic response].
  • Upon re-exposure to the allergen, the allergen binds to IgE on the surface of basophils resulting in degranulation [effector phase].

Binod G C

I'm Binod G C (MSc), a PhD candidate in cell and molecular biology who works as a biology educator and enjoys scientific blogging. My proclivity for blogging is intended to make notes and study materials more accessible to students.

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